@@ -171,6 +171,7 @@ extern void put_online_cpus(void);
#define hotcpu_notifier(fn, pri) cpu_notifier(fn, pri)
#define register_hotcpu_notifier(nb) register_cpu_notifier(nb)
#define unregister_hotcpu_notifier(nb) unregister_cpu_notifier(nb)
+void clear_tasks_mm_cpumask(int cpu);
int cpu_down(unsigned int cpu);
#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
@@ -10,6 +10,7 @@
#include <linux/sched.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
+#include <linux/oom.h>
#include <linux/export.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
@@ -171,6 +172,23 @@ void __ref unregister_cpu_notifier(struct notifier_block *nb)
}
EXPORT_SYMBOL(unregister_cpu_notifier);
+void clear_tasks_mm_cpumask(int cpu)
+{
+ struct task_struct *p;
+
+ read_lock(&tasklist_lock);
+ for_each_process(p) {
+ struct task_struct *t;
+
+ t = find_lock_task_mm(p);
+ if (!t)
+ continue;
+ cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
+ task_unlock(t);
+ }
+ read_unlock(&tasklist_lock);
+}
+
static inline void check_for_tasks(int cpu)
{
struct task_struct *p;
Many architctures clear tasks' mm_cpumask like this: read_lock(&tasklist_lock); for_each_process(p) { if (p->mm) cpumask_clear_cpu(cpu, mm_cpumask(p->mm)); } read_unlock(&tasklist_lock); The code above has several problems, such as: 1. Working with task->mm w/o getting mm or grabing the task lock is dangerous as ->mm might disappear (exit_mm() assigns NULL under task_lock(), so tasklist lock is not enough). 2. Checking for process->mm is not enough because process' main thread may exit or detach its mm via use_mm(), but other threads may still have a valid mm. This patch implements a small helper function that does things correctly, i.e.: 1. We take the task's lock while whe handle its mm (we can't use get_task_mm()/mmput() pair as mmput() might sleep); 2. To catch exited main thread case, we use find_lock_task_mm(), which walks up all threads and returns an appropriate task (with task lock held). Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org> --- include/linux/cpu.h | 1 + kernel/cpu.c | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+)